Browsing by Author "Wang, Yuxuan"
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Item A Better Tropospheric Aerosol Analysis and Forecast Using Data Assimilation and Coupled Modeling(2021-12) Jung, Jia; Choi, Yunsoo; Jiang, Xun; Wang, Yuxuan; Wong, David C.Chemical transport models are useful to predict air pollutant concentrations and provide advice to people to minimize adverse impacts of high levels of tropospheric aerosols and ozone. This dissertation incorporated a coupled model between meteorology and air quality, as well as data assimilation techniques to get more complexity and reliability of chemical transport models. In the first chapter, we assimilated the GOCI AOD into the WRF-CMAQ two-way coupled model over East Asia during the KORUS-AQ period. Improvement of modeling performance on aerosol simulations enabled us to accurately quantify the impact of direct effects of aerosols. Stabilized atmospheric conditions increased most of the gaseous and aerosol pollutants at the surface by 7.87 – 34%. In the second chapter, we showed that the direct effects of aerosols enhanced the strength of the radiation sea fog over the Yellow Sea due to lower temperatures. We found dominant changes in inorganic aerosols at an altitude of 150 m through the aqueous-phase chemistry (~12.36% and ~3.08% increases for sulfate and ammonium) and loss via the wet deposition process (~-3.79% decrease for nitrate). In the third chapter, to estimate top-down NOx emissions over East Asia, we applied an inverse modeling technique with tropospheric NO2 column from TROPOMI in the spring of 2019. We found a substantial contribution of the transported air pollutants on local NOx (22.96 – 35.24%) and O3 (24.23 – 42.26%) budgets. The enhanced chemical loss of NOx compensated for increases by transport, as well as the increased vertical gradient of MDA8 O3 amplified vertical transport and dry deposition processes. In the last chapter, to examine changes in the O3 chemical production regime over the CONUS in the summers of 2011, 2014, and 2017, top-down emissions of NOx and NMVOCs were estimated by using tropospheric NO2 and total HCHO columns from OMI. The inversion suggested 2.33 – 2.84 times higher NOx over the CONUS and 0.28 – 0.81 times fewer NMVOC emissions over the southeastern U.S. We found major metropolitan areas shifted toward NOx-limited conditions. However, meteorological changes caused a significant reduction in the HCHO column over the southeastern U.S, thus the region becoming sensitive to VOC emissions.Item Application of Deep Learning for Air Quality Predictions, Remote Sensing Processing and Long-term Climate Index Forecasting(2021-12) Lops, Yannic; Choi, Yunsoo; Jiang, Xun; Wang, Yuxuan; Eick, Christoph F.The advancement and development of new technology provide atmospheric scientists and modelers to acquire an overwhelming amount of data on meteorology and air quality from space, numerical simulations, and in-situ monitoring sites. Integrating these data sources provides unique opportunities to enhance understanding of atmospheric processes to better simulate and forecast these processes. While Global Climate Models and Chemical Transport Models have undergone significant optimizations and improvements over the past decades, they are still unable to provide fully reliable biogenic air quality predictions or long-term climate forecasting. These limitations can be alleviated and addressed by incorporating in-situ measurements and remote sensing products into data assimilation or reanalysis techniques. While ground-based remote sensing measurements provide detailed point observations, they lack the spatial coverage of remote sensing-derived measurements. Unfortunately, these remote sensing measurements experience issues caused by outside factors such as cloud cover contamination and false reflectance. Internal issues involve sensor errors that corrupt or lead to failed measurements of the data. This study utilizes the advanced capability of several deep learning models for the forecasting of pollen concentrations by up to 7 days; the imputation of remote sensing measurements spatially with partial convolutional neural networks and subsequent revision to incorporate spatio-temporal imputation; and long-term forecasting system of the climate index Nino3.4 by up to 36 months.Item Assessing the Impact of Emission Control Measures on Air Quality and Human Health using Numerical Models, Statistical Analysis, and Machine Learning Approach(2023-12) Mousavinezhad, Seyedali; Choi, Yunsoo; Jiang, Xun; Wang, Yuxuan; Lee, KyoThis dissertation examines the effects of past and prospective mitigation strategies on air quality from regional and health standpoints. In Chapter 1, we analyze in-situ measurement data to discern trends in surface ozone and NO₂ concentrations across major megacity clusters in China from 2015 to 2019. Our findings highlight a concerning increase in daily maximum 8-hour average (MDA8) ozone levels across most regions, with meteorology and precursor emissions being significant contributors to this rise. The study urges a reduction in NOx and VOCs to negate the adverse meteorological effects on ozone concentrations, aiding in the formulation of effective regional air pollution control policies. In Chapter 2, we deploy quantile regression to assess the impact of emission control measures across various climatic regions in the Contiguous United States between 1991 and 2020. Despite a nationwide decline in adjusted ozone concentrations, climate variability threatens to undermine these achievements. The machine learning (SHAP) analysis outlines the meteorological factors chiefly influencing ozone levels in different regions, guiding future emission reduction strategies. Chapter 3 investigates the repercussions of diverse electrification and emission mitigation scenarios on PM2.5 and ozone levels in major U.S. cities. We note a general reduction in PM2.5 with increased electrification but also pinpoint potential hikes in secondary organic aerosols (SOA) and ozone levels. The research proposes region-specific policies, emphasizing the need to curb VOC emissions to enhance the benefits of electrification. In the final chapter, we delve into the health implications of short-term exposure to ozone, spotlighting a notable decrease in premature deaths in the Northeast and Ohio Valley regions due to emission reduction policies. The study recognizes the health and economic gains from integrating EVs, yet warns of potential setbacks, thereby urging a continual reassessment of policies to accommodate dynamic urban scenarios and pollutant complexities. Our comprehensive analysis underscores the critical role of strategic emission controls in enhancing air quality and public health, advocating for adaptive, region-specific policies informed by detailed trend analyses and scenario evaluations. It offers pivotal insights for refining current approaches to air quality management, emphasizing the nuanced challenges posed by changing climatic conditions and urban dynamics.Item Atmospheric Composition Changes During Droughts in the Continental U.S.(2023-04-22) Li, Wei; Wang, Yuxuan; Jiang, Xun; Flynn, James H., III; Li, LimingThe abnormal meteorological conditions under droughts can impose large changes in atmospheric compositions. In this dissertation, we quantified these changes using long-term atmospheric composition observations over the continental U.S. during summertime. Specifically, we revealed the spatial east-west variation in ozone (O3) response to drought: higher O3 enhancement in the southeast U.S. (SEUS) and no significant change or even a decrease in the west. We attributed this spatial discrepancy to O3 chemistry caused by the opposite response of isoprene: a 37% decrease in isoprene under exceptional drought in California in contrast to a 41% increase in Georgia. The enhanced isoprene in the SEUS also contributes to the 24% higher value of organic aerosol (OA), which can be largely attributed to the increase of isoprene epoxydiols derived secondary organic aerosol (IEPOX SOA) with a high dependence on sulfate. The elevated OA in the Pacific Northwest under droughts is caused by increasingly higher wildfire emissions. We evaluated the chemical transport model GEOS-Chem regarding its capability in capturing the observed drought-air pollution relationships. The model under- and overestimates the drought-induced O3 and OA changes in the SEUS, respectively, which can be partly caused by the overprediction of biogenic isoprene emissions. A satellite-derived drought stress factor by minimizing the model-to-observed bias of formaldehyde column to temperature sensitivity was implemented in GEOS-Chem. The resulted reduction in isoprene emissions can lower the OA positive bias by 7%-12% and improve the O3 enhancement by 1-3 ppb over low-NOx regions. We also found a decrease of 11% in surface fine dust over the SEUS under droughts in contrast to the expected increase in other regions. Through the teleconnection to the negative North Atlantic Oscillation, a lower-than-normal and more northeastward displacement of the Bermuda High is present during SEUS droughts, resulting in less dust being transported into the SEUS. The enhanced precipitation in the Sahel associated with the northward shift of the Intertropical Convergence Zone also leads to lower dust emissions therein. The GEOS-Chem model can capture the weakened African dust transport and reproduce the reduced dust in the SEUS while misses the enhanced dust in the western areas.Item Atmospheric Ozone, Mercury, and Biomass Burning in South-Central Texas(2016-08) Liu, Lei 1989-; Talbot, Robert W.; Jiang, Xun; Wang, Yuxuan; Khan, Shuhab D.This study investigated atmospheric ozone, mercury, and biomass burning characteristics in south-central Texas. I examined the past twenty-three years of ground-level O3 data and selected meteorological parameters in Houston, and found the frequency of southerly flow has increased by a factor of ~2.5 over the period 1990–2013, likely suppressing O3 photochemistry and leading to a “cleaner” Houston environment. The sea breeze was enhanced greatly from 1990 to 2013 due to increasing land surface temperatures, increased pressure gradients, and slightly stronger on-shore winds. Long-term continuous measurements of atmospheric mercury, meteorological parameters, and key trace gases were conducted in Houston, Texas under urban and coastal marine settings. At the urban site, gaseous elemental mercury (GEM) mean value was 185 ppqv and 165 ppqv at the coastal site. The urban site had a greater occurrence of high mercury events than the coastal site. A variable mercury diurnal pattern was found: At the urban site, GEM showed a maximum mixing ratio before sunrise and the minimum mixing ratio in late afternoon. At the coastal site, GEM decreased at night and reached its minimum before sunrise. The relationship between mercury species and meteorological factors was studied. The concurrence of GEM, CO2, CO, CH4, and SO2 maximum values were striking. A prescribed grassland fire experiment was conducted employing in-situ field sampling combined with comprehensive pre-burn and post-burn sampling. The volatile organic compounds (VOCs) exhibited a double peak feature in the flaming and smoldering stages. The emission of VOCs was associated primarily with the smoldering combustion stage and correlated better with CO than with CO2. The emission factors of CO2, CO, CH4, NO, CH3Cl, C2H6, C2H4, C3H8, C3H6, C6H6, and C7H8 accounted for 96% of the total species. Total gaseous mercury was released primarily during the smoldering phase, although the total amount released from the fire was small (0.015 kg). Overall, 53,257 kg CO2 was emitted into the atmosphere during the fire and it accounted for 95% of all species emissions. The relationship between carbon emissions from the dry fuel (194 tons) and released from CO2 (14.5 tons) was found to be 7.5% for this event.Item Impact of Biomass Burning on Regional Air Quality and Weather Patterns in Texas(2019-05) Wang, Sing-Chun 1992-; Wang, Yuxuan; Talbot, Robert W.; Jiang, Xun; Hu, YandiFires are one of the most important sources of aerosol and pollutant gases. The influence of fires on the atmosphere concerns not only air quality but also weather patterns. Large uncertainties still exist in our quantitative understanding of how fires will both affect and respond to changes in weather and climate. Motivated by this knowledge gap, the present thesis aims to provide a better understanding of the effects of fire-emitted pollutants on air quality and weather patterns over Texas. This thesis examined the influence of fire pollutants, from both long-range transport and local wildfires, on Texas air quality and weather patterns. Using the GEOS-Chem passive tracer simulation, we quantified that the long-range transport of Central American fire emissions contributes an enhancement of 9-12 ppbv in maximum daily average 8-hr (MDA8) ozone and of 3-4 g/m3 in daily PM2.5 in Texas cities along the Gulf Coast. With respect to local wildfires, we first developed a quantile regression model to predict monthly wildfire burned area in Eastern Texas for two peak fire seasons during 2003-2015. Key predictors of wildfires for this region were identified and ranked by the model; they include drought, climatic anomaly of minimum relative humidity and maximum temperature, and climatology of precipitation. Applying the projected meteorological fields from the Coupled Models Inter-comparison Project (CMIP5), the fire prediction model projects that future median and 95th percentile burned area will decrease by 25% and increase by 24%, respectively. The reduction of the burned area at the median level is mainly driven by increasing relative humidity anomaly, while the enhancement of the 95th percentile burned area is mostly caused by rising temperature anomaly in the midcentury. Lastly, increasing fire emissions were implemented in the single column model (SCM) of version 6 of the Community Atmosphere Model (CAM6) to investigate the influences of fires on weather patterns over the Houston area. Increased fire emissions would cause larger influences on shortwave radiative fluxes and planetary boundary layer height under dry conditions, which are further extended to meteorological factors such as temperatures and relative humidity in the lower atmosphere and to precipitation under dry conditions.Item Investigation of Methane Emissions and Sources(2018-08) Yang, Shuting 1987-; Talbot, Robert W.; Jiang, Xun; Wang, Yuxuan; Choi, Yunsoo; Frish, Michael B.Methane (CH4) is an important trace gas and the most potent greenhouse gas in the global atmosphere. This study addressed CH4 related issues using a multi-pronged approach to monitor, characterize, and quantify CH4 emissions and sources through three observational platforms including Remote Methane Leak Detector mounted on an Unmanned Aerial Vehicle (RMLD-UAV), the UH mobile laboratory, and the Moody tower stationary site. The RMLD-UAV system provided an advanced capability in detecting CH4 leaks autonomously in the natural-gas industry. A quantification algorithm was derived based on a mass-balance approach, which was accurate to approximately 50% under preferred wind conditions with higher wind speeds and lower wind variation. The influence of systematic error was investigated by introducing simulated noises, of which GPS noise presented the greatest impact on leak rate errors. Zero-leak cases can be ascertained via a skewness indicator which is unique and promising. Key information concerning regional anthropogenic CH4 sources was obtained through the stable carbon isotope δ13CCH4 during two field campaigns in Texas using a state-of-the-art mobile laboratory. The background δ13CCH4 signatures and overall CH4 distributions depicted the different dominate CH4 sources in the studied areas. δ13CCH4 signatures of thirty-three sources were identified varying from -76‰ to -23‰. Several repeated measurements revealed the variability of typical source signatures. The detection of an unexpected CH4 leaking demonstrated the capability of the system that can capture and identify unknown CH4 leaks. One-year continuous measuring of CH4 mixing ratios and related meteorological factors conducted at the Moody Tower site indicated the relative long-term seasonal and diurnal dynamics of regional CH4. The diurnal variation of CH4 in different seasons showed the same trend with the highest values happened in the early morning and lower values during the daytime. The calculated δ13CCH4 signature was -58.9‰ yearly and was diverse in different seasons. The prevailing wind was southerly; whereas, most of the high CH4 spikes came from the northeast of the site where the polluted ship-channel area is located. The results of this study supplied valuable references for regulatory programs, regional emission inventories, and atmospheric model inputs.Item Meteorological Influences on Surface Ozone in the Houston-Galveston-Brazoria Region(2023-04-18) Griggs, Philip; Wang, Yuxuan; Flynn, James H., III; Jiang, Xun; Kotsakis, AlexanderVarying meteorology within the complex coastal subtropical environment of the Houston- Galveston-Brazoria (HGB) region has emerged as a driving factor of surface ozone concentrations, which are harmful to human health. Thus, analysis of ozone trends around common meteorological events as well as routine collection of air quality data in unmonitored over water areas drives a more complete understanding of the influence meteorology has on high ozone events in the HGB region. Chapter 1 describes the deployment of three boats outfitted with ozone and meteorological instruments to the Gulf of Mexico and Galveston Bay for the Galveston Offshore Ozone Observations (GO3) and Tracking Aerosol Convection Interactions ExpeRiment - Air Quality (TRACER-AQ) field campaigns from July-October of 2021 to address the observational gap in over water air quality data needed to verify and improve photochemical modeling. During these campaigns, over 600 mobile hours were logged including 134 missions and 35 ozonesondes launched throughout Galveston Bay and the Gulf of Mexico. Several periods of ozone exceeding 100 ppbv were observed over the waters of Galveston Bay and the Gulf of Mexico during the operational period. Chapter 2 examines the relationship between mesoscale circulations and surface ozone in the HGB area between 2020-2022. The HGB area was found to have a strong correlation between mesoscale circulations and maximum daily 8-hour (MDA8) ozone exceedance days with 91% of exceedance days exhibiting a bay breeze or mesoscale induced storm. Additionally, a unique feature of rapid ozone enhancement coincident with the passage of mesoscale boundaries was analyzed. Chapter 3 discusses the development of a novel method for clustering North Atlantic tropical cyclones (TC) from 2010-2021 using a k-means algorithm for the purpose of relating the time-period around the landfall of a TC in North America to MDA8 ozone exceedances in the HGB area. Landfall locations along the east coast of the United States were found to produce the highest MDA8 ozone values in the HGB area, with an average maximum MDA8 ozone value in the region of 101 ppbv in the 0-2 day period after landfall.Item Simulating the Effects of Hydroclimate Stress on BVOC-Chemistry-Climate Interactions in NASA GISS ModelE(2022-07-08) Klovenski, Elizabeth Renee; Wang, Yuxuan; Jiang, Xun; Flynn, James H., III; Bauer, Susanne E.; Tsigaridis, KostasDrought is a hydroclimatic extreme that causes perturbations to the terrestrial biosphere which causes biosphere-atmosphere feedbacks. Drought acts as a stressor on vegetation, which causes a unique biogenic volatile organic carbon (BVOC) emission response during severe or prolonged drought. In the first chapter, we introduce the concept of drought and the four main types: meteorological, agricultural, hydrological, and socioeconomic. Then we expand upon how drought affects vegetation on the physiological level and how drought stress impacts vegetative isoprene emissions and their impact on atmospheric composition and climate, as isoprene is the dominantly emitted BVOC and is a precursor to ozone (O3) and secondary organic aerosols (SOA). In the second chapter, the implementation of isoprene drought stress into the Model of Emissions and Gases and Aerosols from Nature (MEGAN) module in the NASA GISS ModelE, an earth system model, is described along with validation of isoprene emissions during the 2012 drought at the Missouri Ozarks Ameriflux site. In the third chapter, the development of a model tuned isoprene drought stress parameterization is described along with validation of O3, PM2.5 and HCHO tropospheric columns compared to observations during drought periods. We found the isoprene drought stress parameterization reduced the normalized mean bias in tropospheric HCHO column, a proxy for isoprene emissions, by ~ 19.3% in the southeast U.S. during the 2007 drought and ~ 15.3% during the 2011 drought. In the fourth chapter, the ModelE tuned isoprene drought stress ( ) parameterization is applied in free-running experiments to simulate the historic 1950s decadal drought that occurred from 1948-1957 and in present-day experiments from 2003-2013. It was found the inclusion of isoprene drought stress in both the historic and present-day experiments reduced the averaged precipitation in the warm season (APR-SEP) and reduced the frequency of “rainy-days”. With decreasing isoprene emissions and decreasing SOA during drought, its theorized a biosphere- atmosphere feedback is causing reduced precipitation during the warm season through BVOC- drought-aerosol-climate interactions. We speculate that this feedback during our simulations is exacerbating the already existing precipitation deficit during drought periods.Item Spatiotemporal Variability of CO2, Solar-Induced Fluorescence, And Precipitation Over the Tropical Rainforests(2023-08) Albright, Ronald Joe; Jiang, Xun; Li, Liming; Wang, Yuxuan; Choi, YunsooTropical rainforest ecosystems change forest dynamics during the dry/fire season, transitioning from an atmospheric CO2 sink to a CO2 source. The Amazon basin, Congo basin, and the tropical Indo-Pacific play vital roles in biospheric processes, which contribute to Earth’s atmospheric CO2 concentration. This investigation will use various space-based and ground-based datasets and empirical models to explore photosynthetic activity, spatiotemporal variability, and correlation among critical variables (e.g., Solar-induced chlorophyll fluorescence (SIF), CO2, precipitation, high vapor pressure deficit (VPD), and burned areas). Specifically, we use Orbiting Carbon Observatory 2 (OCO-2) SIF, OCO-2 CO2, Global Precipitation Climatology Project (GPCP) precipitation, Moderate Resolution Imaging Spectrometer (MODIS) burned area, and CarbonTracker Model. Over the entire Amazon basin from September 2014 to December 2019, we found a positive temporal correlation (0.94) between OCO-2 SIF and GPCP precipitation and a negative temporal correlation (–0.64) between OCO-2 SIF and OCO-2 CO2. These findings suggest that precipitation enhances photosynthesis, thus resulting in higher values for SIF and the rate of removal of atmospheric CO2 in the Amazon region. We also identify seasonal variations in the spatial distributions of these variables across the Amazon region. Over the Congo basin, during the same timeframe (Sep 2014-Dec 2019), we find that the atmospheric CO2 is ~2 ppm higher than the regional background during the boreal summer (June–August), primarily due to biomass burning and significantly reduced photosynthetic activities during the dry season. Over the tropical Indo-Pacific, we explore the spatial distributions of SIF, CO2, and precipitation during El Niño events verse other months. The CarbonTracker Model is employed to assess the impact of El Niño on atmospheric CO2. Various datasets of deseasonalized precipitation, deseasonalized SIF, and deseasonalized CO2 are analyzed in time series averaged over 10S-10N, 100E-160E. We have discovered that there is less precipitation, more sinking air, lower SIF, and higher CO2 over the Indo-Pacific region during the El Niño events. The CarbonTracker model can simulate the increase of atmospheric column CO2 during the El Niño event, although there are some difficulties in capturing the correct spatial distribution of CO2 anomalies. These findings suggest that improved seasonal fire management practices in these tropical regions are critical components needed to achieve successful and timely reductions in global carbon emissions, as set forth by international agreements.Item Spatiotemporal Variations Of Saturn's Zonal Winds Based On Cassini Long-term (2004-2017) Multi-Instrument Observations(2020-05) Studwell, Aaron Mark; Li, Liming; Jiang, Xun; Choi, Yunsoo; Wang, Yuxuan; Wood, Lowell T.The observations of Saturn by the Cassini mission spanned thirteen years (2004-2017) and provided scientists data and images that will expand our knowledge for decades to come. This dissertation is divided into four tasks: 1) Develop and validate a more general form of thermal wind equation (TWE), which does not apply the assumptions used in the classical TWE; 2) Apply the new TWE to study the spatiotemporal patterns of the atmospheric winds above the visible cloud layer, ~1 to 500 mbar; 3) Develop a global profile of the atmospheric winds below the visible cloud layer, ~1,000 to 3,000 mbar; and 4) Utilize atmospheric winds to investigate Saturn’s 2010 Great White Storm with particular attention to its asymmetric development. The results from Tasks 1, 2 and 3 provides a relatively complete picture of the seasonal variations of Saturn’s winds. Some important characteristics of Saturn’s winds are revealed: (1) The global profile of zonal winds in the deep troposphere is generated for the first time; (2) In the polar region, the 2,000-mbar winds undergo temporal variation; (3) Within the visible cloud layer, the zonal winds did not significantly change between 2009 and 2015; and (4) The stratospheric equatorial zonal jets weakened from ~500 m s-1 in 2009 to 0 m s-1 in 2015. This is the first systematic analysis of the seasonal changes of Saturn’s zonal winds across both the troposphere and stratosphere, expanding our understanding of spatiotemporal variations of Saturn’s atmosphere. In particular, the vertical structure and its changes over time yield new insight on the atmospheric dynamics (e.g., stability), which in turn aid in the development of new theories and models of the atmospheric systems of the giant planets. In Task 4, the wind field and the associated vorticity field are used to investigate 2010 Great White Storm. Specifically, during the mature phase of this event, the associated bright clouds expanded significantly equatorward, but its poleward growth was limited. The analysis of the wind and vorticity fields suggest that large meridional gradients of quasi-geostrophic potential vorticity, acting as a barrier to cloud mixing, was a factor in the asymmetric expansion.Item Synthesis Analysis of Multi-dimensional Ozone measurements in Coastal Environments Toward Improving Simulations and Advancing Satellite Products(2023-08) Bernier, Claudia; Wang, Yuxuan; Gronoff, Guillaume P.; Berkoff, Timothy A.; Jiang, Xun; Estes, Mark; Flynn, James H., IIIIn order to improve the comprehension and forecasting of spatio-temporal variations of surface ozone, it is essential to combine chemical transport model (CTM) simulations with measurement data. The purpose of this thesis is to investigate air quality variability in coastal regions using the cross-validation of CTMs, high quality multi-dimensional lidar data, surface measurements, and satellite retrievals. This study first evaluates diurnal ozone patterns in the Houston-Brazoria- Galveston (HGB) region using a clustering method to better understand meteorological patterns (Bermuda High and Low-level jet) and their interaction with ozone variability. Results demonstrated the ability of the clustering method to group ozone variability more accurately than a simple method tested and showed clear meteorological influence based on the different clusters. Next, we utilize multi-dimensional measurements from ozone lidar in conjunction with both an offline GEOS-Chem CTM simulation and the online GEOS-Chem simulation, GEOS- CF, to investigate spatio-temporal variations of coastal ozone during three air quality campaigns: 2017 Ozone Water-Land Environmental Transition Study (OWLETS)-1, 2018 OWLETS-2, and 2018 Long Island Sound Tropospheric Ozone Study (LISTOS). The cluster results effectively capture and emphasize the diverse temporal and vertical variations observed in multiple cases throughout the campaign periods. Results indicate both models struggle to simulate mid-level ozone (2000 - 4000 m) and a generally weak agreement to the lidar (R = 0.12 and 0.22, respectively). Both models have a good agreement (R ≈ 0.70) in the low-level altitude range (0 - 2000 m). Finally, we investigate regional impacts of anthropogenic emissions on tropospheric ozone during a recent campaign, Tracking Aerosol Convection ExpeRiment – Air Quality (TRACER-AQ) using the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem) at a fine resolution (4 km), ozone lidar observations, surface monitoring stations, and Tropospheric Monitoring Instrument (TROPOMI) nitrogen dioxide vertical column densities. Results reveal the model is better able to capture mid-level/free tropospheric ozone and underestimates surface/boundary layer ozone during two episodes. The results also reveal an underestimation of simulated nitrogen dioxide levels in urban areas, as well as over the Galveston Bay/near the Gulf coast, potentially attributable to discrepancies in modeled emission sources.Item The Radiant Energy Budgets of Titan and Mars(2022-11-21) Creecy, Ellen Catherine; Li, Liming; Jiang, Xun; Wang, Yuxuan; Choi, Yunsoo; Nixon, Conor A.The radiant energy budget of planets and moons is of wide interest in the fields of geoscience and planetary science, as it is essential to understanding surface and atmospheric processes. In this work, we report the seasonal variations of the energy budget for both Titan and Mars and examine the surface emissivity of high latitude regions on Mars. Based on the Cassini multi-instrument observations, we find the global‐average emitted power decreased by 6.8 ± 0.4%, while the absorbed solar power decreased 18.7% ± 0.5% during the Cassini period (2004–2017). We find Titan's radiant energy budget is not balanced from 2004 to 2017, with the absorbed solar energy being (1.208 ± 0.008) x 10^23 J and the emitted thermal energy being (1.174 ± 0.005) x 10^23 J. There is an energy imbalance of 2.9 ± 0.8% of the emitted thermal energy. Titan's global radiant energy budget is not balanced at the timescales of Earth's years and Titan's seasons, and the imbalance can be beyond 10% of the emitted thermal energy at the timescale of an Earth year. Based on the observations from Mars Global Surveyor, Curiosity, and InSight, we find Mars’ global-average emitted power is 111.7 ± 2.4 Wm-2. There are strong seasonal variations in the emitted energy, and energy imbalances at the time scale of Mars’ seasons (e.g., ∼15.3% of the emitted power in the Northern autumn for the Southern Hemisphere), which could play a role in generating dust storms on Mars. We find the 2001 global dust storm decreased the global-average emitted power during daytime but increased the global-average emitted power at nighttime. This suggests that global dust storms play a significant role in modifying Mars’ radiant energy budget. Using data from the Mars Climate Sounder, we compute a solid-angle integrated emissivity and relative emissivity for the Southern and Northern high latitude regions, respectively, with 5 degree resolution in latitude and 10 degree resolution in longitude. We find the solid-angle integrated emissivity is typically a few percent less than the emissivity at nadir, with no strong correlation to known surface features (e.g., cryptic vs. anti-cryptic terrain).Item Trends, Sources, and Formation Pathways of Tropospheric Ozone across Southeast Texas(2023-08) Soleimanian, Ehsan; Wang, Yuxuan; Jiang, Xun; Flynn, James H., III; Walter, Paul J.Tropospheric ozone poses significant risks to human health, climate, and agriculture. This dissertation examines long-term variations in ambient levels, sources, and formation mechanisms of surface ozone in the Houston-Galveston-Brazoria (HGB) region. We investigated the reduction in maximum daily 8-hour average ozone (MDA8 O3) levels from 2000 to 2019 and evaluated the impact of emission control policies targeting nitrogen oxides (NOx) and volatile organic compounds (VOCs). By utilizing the positive matrix factorization (PMF) model, regional background ozone was identified as the major contributor to MDA8 O3, followed by natural gas/fuel evaporation, solvent/painting/rubber industries, engine combustion, and petrochemical emissions. Notable reductions in contributions from petrochemical emissions, engine combustion, and natural gas/fuel evaporation were observed, authenticating the effectiveness of emission control policies. In addition to a diverse range of emission sources, meteorology plays a crucial role in driving ozone level exceedances in Southeast Texas. We investigated transport pathways and photochemical formation contributing to ozone exceedances during the TRACER-AQ campaign in September 2021. The trajectory analyses using HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) tool and FLEXible PARTicle (FLEXPART) dispersion model revealed ozone pollution episodes were associated with the transport of air masses from the central/northern US, with local recirculation and pollutant accumulation exacerbating ozone exceedances in Houston. By implementing the Comprehensive Air Quality Model with extensions (CAMx), ozone production hotspots were identified over Houston city and industrial districts of HSC during pollution episodes. Ozone production rates were generally influenced by transported VOC-rich air masses, leading to a transition in ozone formation tendency from VOC-limited to NOx-limited conditions. However, local NOx emissions in Houston maintained a VOC-limited regime. Elevated ozone production along the transport pathways also contributed to ozone exceedances in the region. Through these investigations, this dissertation enhances our understanding about the long-term contribution of different sectors in ozone formation as well as the complex relationship between transport patterns and photochemical formation of ozone in the HGB region during pollution events. The findings provide valuable insights into the synergy between local emissions, transport patterns, and ozone production for developing more precise and tailored policies to further mitigate ozone pollution in Houston.